1. Field of the Invention
The present invention relates to an oil supply apparatus of a four-stroke-cycle engine for use mainly on a portable work machine.
2. Discussion of the Background
A portable work machine such as a chain saw, a lawn mower or a mower is generally mounted with a two-stroke-cycle engine since this type of engine has advantages such as a simple structure and light weight. The two-stroke-cycle engine, however, has disadvantages in that there are large amounts of CO, HC in exhaust gases thereof. This is a problem for cleaning engine exhaust gases and environmental protection.
A four-stroke-cycle engine has advantages with respect to avoiding air pollution since the amount of CO, HC of this type of engine is small compared with the two-stroke-cycle engine. Recently, therefore, investigations have been conducted on the mounting of the four-stroke-cycle engine on the portable work machine such as the chain saw, the lawn mower and the mower.
The portable work machine, such as the chain saw and the mower, is tilted in various directions during operation, so that the engine mounted on the portable work machine is also tilted in various directions. Thus, the engine mounted on the portable work machine pitches and rolls during operation. Such slants of the engine are not serious for the two-stroke-cycle engine. It is, however, serious for the four-stroke-cycle engine. This is because oil can not be supplied to several parts of the engine if the four-stroke-cycle engine is tilted. More specifically, an oil surface of an oil reservoir fluctuates according to slants of the engine. Then, an oil inlet of an inlet pipe, which inhaled or sucked the oil from the oil reservoir, rises above the oil surface. Thus, the oil can not be supplied to several parts of the engine. Considering this disadvantage, a four-stroke-cycle engine adapted to be mounted on the portable work machine has been developed. Such a four-stroke-cycle engine is disclosed in Japanese Utility Model Laid-Open No. Hei 4-93707, Japanese Patent Laid-Open No. Hei 8-260926 and Japanese Patent Laid-Open No. Hei 9-228816.
Japanese Utility Model Laid-Open No. Hei 4-93707 discloses a four-stroke-cycle engine having an oil pan with a contrivance. According to the contrivance of the oil pan, oil leakage from the oil pan does not occur if the four-stroke-cycle engine is tilted within a certain range. This four-stroke-cycle engine has a splash type oil supply system, which splashes the oil by an oil dipper provided with a connecting rod. The four-stroke-cycle engine disclosed in Japanese Utility Model Laid-Open No. Hei 4-93707, however, has a disadvantage in that big oil leakage from a blowby gas exhaust passage occurs in the inverted position of the engine. Also, a piston and a crank shaft would be soaked in oil in the inverted position of the engine. When the piston and the crank shaft are soaked in the oil, the power of the four-stroke-cycle engine is seriously decreased due to resistance of the oil. It is, therefore, difficult to use the portable work machine in a position that inverts the four-stroke-cycle engine.
A four-stroke-cycle engine disclosed in Japanese Patent Laid-Open No. Hei 8-260926 circulates the oil through a crank chamber, an oil chamber and a valve chamber using pressure fluctuation of the crank chamber caused by reciprocation of a piston. It is, however, not capable of returning the oil from the crank chamber to the oil chamber and from the valve chamber to the crank chamber when the four-stroke-cycle engine is inverted. It is, therefore, difficult to use the portable work machine for a long period of time in the position that inverts the four-stroke-cycle engine.
Japanese Patent Laid-Open No. Hei 9-228816 discloses an invention of an oil supply apparatus of a four-stroke-cycle engine for inhaling the oil compulsively from an oil reservoir in an oil tank by an oil pump. The oil supply apparatus comprising: an inhaling pipe for inhaling the oil from the oil reservoir, the inhaling pipe having an oil inhaling inlet rotatably supported around a crank shaft of the engine and a perpendicular axis of the crank shaft, and a weight attached to the inhaling pipe adjacent to the oil inhaling inlet, wherein the oil inhaling inlet is always urged to the direction of the gravity by the weight. It is, however, necessary to provide a mechanism for rotating the oil inhaling inlet in two directions and a sealing mechanism for supporting the rotating mechanism airtightly in an oil pan, for the oil supply apparatus. Thus, the oil supply apparatus has several disadvantages such as a complex structure, increasing the number of parts, the large sizing of the apparatus, and increasing of weight. Especially, the large sizing of the apparatus and the weight increase are serious for a portable work machine mounted with the four-stroke-cycle engine since a load imposed on an operator will increase.
Further, in general, a four-stroke-cycle engine has a disadvantage in that too much oil is supplied when the liquid oil is supplied directly to inside of the engine such as to the crank chamber and the valve chamber. In this case, excessive oil gives resistance to smooth rotation and slide movement of the rotating parts and sliding parts, then, engine power will be less. Thus, a four-stroke-cycle engine that supplies the oil in mist condition to the inside of the engine is originated. For example, Japanese Patent Laid-Open No. Hei 9-228816 discloses such a four-stroke-cycle engine. This engine comprising: a crank shaft disposed in an oil tank, and an oil slinger fixed to the crank shaft, wherein whipping of the oil according to rotation of the oil slinger in the oil tank, then, the oil in the mist condition is generated.
However, the four-stroke-cycle engine disclosed in Japanese Patent Laid-Open No. Hei 9-228816 has the following disadvantages. Great resistance is given to the oil slinger when the oil slinger whips the oil. Thus, the engine power will be less due to the resistance of the oil slinger. Since the oil tank and the crank case should be formed side by side, the size of the engine along the crank shaft will be increase, then, the size of the engine itself will be increased.